Although the invention will be disclosed as embodied in a fishing rod, it will become evident that the principles of the invention may be embodied in such objects as vaulting poles, whip antennas, flag poles, and other structures of a cantilever nature when the resistance to flexure of the free end is desirable to be increased automatically in proportion to the applied load.
It is recognized by anglers that the resistance to flexure of a fishing rod ideally be proportional to the size of the fish and/or the weight of a lure. For small fish the rod flexes readily and there is no good reason to use an oversized rod where a small one will do. Analogously, large fish are best caught with a large rod. However, in order to handle the larger fish as well as those which are smaller, the fisherman will frequently overburden himself. Consequently, a single rod having variable performance is a desirable objective.
Attempts have been made to attain the foregoing objective by the use of a hollow rod equipped with a longitudinally-manually-shiftable plug or core, for example, as disclosed in U.S. Pat. No. 3,570,164. However, in this case, the pliancy of the rod is a step function, depending on the selected relation between the core and body of the rod, whereas I have found that a rod having a smooth transition from a lower to a higher limit is easier to manipulate and responds automatically in a more truly proportional manner. In the said patent, shifting of the core away from or toward the tip consists in locating a tapered core member at one or another predetermined axial position within and transversely spaced from an identically internally tapered rod member. If the core member and rod member are thus spaced apart in all positions of the core member, no augmented resistance to flexure is to be seen and the advantages set forth herein as desirable are not attained.